1. Field of the Invention
The present invention relates to variable valve systems that can vary a valve operational characteristic such as maximum lift quantity and opening/closing timing of an engine valve which is an intake valve or an exhaust valve in an internal combustion engine. More specifically, the invention relates to the variable valve system provided with a lift quantity variable mechanism that can vary the maximum lift quantity of the engine valve.
2. Description of Background Art
A variable valve system of an internal combustion engine provided with a cam provided to a cam shaft is known wherein a rocker arm is rocked by the action of a valve driving force of the cam and a lift quantity variable mechanism varies maximum lift quantity of an engine valve. See, for example, JP-A No. 2002-276315.
In addition, a variable valve system is known wherein a timing variable mechanism is provided with a hydraulic actuator. When the actuator operated according to the supply and the exhaust of hydraulic fluid rotates a camshaft, a phase of the camshaft with a crankshaft of an internal combustion engine is varied and the opening and closing timing of an engine valve is varied. See, for example, JP-A No. 2000-227033.
As the whole rocker arm is moved together with a rocker shaft with the cam shaft provided to a cylinder head of the internal combustion engine in the center by the lift quantity variable mechanism of the variable valve system and a space for moving the whole rocker arm and the rocker shaft is required to be secured around the cam shaft when the maximum lift quantity of the engine valve is varied, the cylinder head is large-sized. As a result, the internal combustion engine is large-sized.
In addition, in the valve system in which the cam opens and closes the engine valve via the rocker arm, it is desirable that the inertia mass of members including the rocker arm between the cam and the engine valve is reduced so as to enhance the responsiveness of opening and closing the engine valve during a high-speed operation of the internal combustion engine.
Further, in the variable valve system in which the maximum lift quantity of the engine valve is continuously varied, as the maximum lift quantity is continuously reduced to approximately zero by the lift quantity variable mechanism when the engine valve is halted, it takes much time since an operated condition in which the engine valve is operated at the large maximum lift quantity till a halted condition or since the halted condition till the operated condition at the large maximum lift quantity and the time lag of switching between the operated condition and the halted condition may increase.
In addition, when the lift quantity variable mechanism is provided with a rocking member that can rock the camshaft to vary the maximum lift quantity, a part for supporting the rocking member is provided to the camshaft or is provided alongside in an axial direction of the camshaft together with a bearing of the camshaft in a cam holder that rotatably supports the camshaft, thereby, the length of the camshaft is extended, and the internal combustion engine may be large-sized in the axial direction of the camshaft in the body (for example, a cylinder head) provided with the camshaft of the engine.
Further, when the variable valve system is provided with a hydraulic actuator that drives the lift quantity variable mechanism, the compact arrangement and the miniaturization of the hydraulic actuator are required in view of the miniaturization of the internal combustion engine.